bugfix: include streaming procedure errors in traces

[cbrewster]

Why

Streaming response procedures don't raise errors like the other procedures, instead the errors are included in the AsyncIterator.

Also fixes issues with using contextvars + async generators.

What changed

• Check if the message from the async iterator is a RiverError, if so, record it on the span
• Use start_span instead of start_as_current_span, the latter resets a contextvar in its finally clause which is invalid to do for async generators as the async generator's finalizers run in a different context
  • Thread the span through manually so we still propagate the tracing info

Test plan

• Should see errors for failed streaming procedures
• Logs about resetting contextvars in a different context should go away
• Added some tests for the otel stuff to make sure the error handling works here

[cbrewster]

Current dependencies on/for this PR:

• main:
  • PR bugfix: include streaming procedure errors in traces #121 👈

This comment was autogenerated by Freephite.

[masad-frost]

@blast-hardcheese can I dump this on you please? :D

[blast-hardcheese]

Trending in the right direction, for sure. Great call-out wrt the asyncio.wait not raising the captured exceptions. In a sense, it can't do that sensibly.

Otoh, this really makes me want a linting rule for "you called a function that returned a value, but you didn't receive it." Kind of challenging in Python due to the dynamic and multipurpose nature of many functions, but it would have caught this.

[blast-hardcheese]

I intended to approve. Pardon.